gh-128042: Emit a `configure warning when -O0 and --enable-optimizations` are combined (#137975)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>
2025-12-23 09:19:18 +00:00 · 2025-08-27 08:00:43 +09:00 · 2025-08-27 08:00:43 +09:00 · ffaec6e2a1
commit ffaec6e2a1
parent 5ae8b97f6b
3 changed files with 16 additions and 0 deletions
--- a/Misc/NEWS.d/next/Build/2025-08-26-21-18-32.gh-issue-128042.5voC8H.rst
+++ b/Misc/NEWS.d/next/Build/2025-08-26-21-18-32.gh-issue-128042.5voC8H.rst
@ -0,0 +1 @@
+``./configure`` now warns when ``--enable-optimizations`` and ``CFLAGS=-O0`` are both set, suggesting removing ``-O0`` from ``CFLAGS`` for optimal performance.  Patch by Taegyun Kim.
--- a/7
+++ b/7
@ -8407,6 +8407,13 @@ fi


 if test "$Py_OPT" = 'true' ; then
+  # Check for conflicting CFLAGS=-O0 and --enable-optimizations
+  case "$CFLAGS" in
+    *-O0*)
+      { printf "%s\n" "$as_me:${as_lineno-$LINENO}: WARNING: CFLAGS contains -O0 which may conflict with --enable-optimizations. Consider removing -O0 from CFLAGS for optimal performance." >&5
+printf "%s\n" "$as_me: WARNING: CFLAGS contains -O0 which may conflict with --enable-optimizations. Consider removing -O0 from CFLAGS for optimal performance." >&2;}
+      ;;
+  esac
  # Intentionally not forcing Py_LTO='true' here.  Too many toolchains do not
  # compile working code using it and both test_distutils and test_gdb are
  # broken when you do manage to get a toolchain that works with it.  People
--- a/configure.ac
+++ b/configure.ac
@ -1823,6 +1823,14 @@ fi],
 [AC_MSG_RESULT([no])])

 if test "$Py_OPT" = 'true' ; then
+  # Check for conflicting CFLAGS=-O0 and --enable-optimizations
+  case "$CFLAGS" in
+    *-O0*)
+      AC_MSG_WARN([m4_normalize([
+        CFLAGS contains -O0 which may conflict with --enable-optimizations.
+        Consider removing -O0 from CFLAGS for optimal performance.])])
+      ;;
+  esac
  # Intentionally not forcing Py_LTO='true' here.  Too many toolchains do not
  # compile working code using it and both test_distutils and test_gdb are
  # broken when you do manage to get a toolchain that works with it.  People
				`@ -0,0 +1 @@`
				``./configure`` now warns when ``--enable-optimizations`` and ``CFLAGS=-O0`` are both set, suggesting removing ``-O0`` from ``CFLAGS`` for optimal performance. Patch by Taegyun Kim.